The present invention relates to a new and improved construction of an apron drafting arrangement comprising a pair of back rolls, a pair of intermediate rolls and a pair of front rolls. A top apron is placed loosely about the top roll of the intermediate pair of rolls and about a respective deflecting guide element which, as seen in the direction of material flow, are located upstream and downstream of the top roll of the intermediate pair of rolls, there being further provided a top apron guide cage for taking-up or housing the top intermediate roll and the deflecting elements.
A three-roll drafting arrangement is already known to the art from German Pat. No. 521,181 wherein the lower run of the top apron is deflected by rigid deflecting elements located upstream and downstream from, and parallel to, the top intermediate roll. The roving subject to draft in this manner is contactingly guided in an arc over a somewhat greater zone of the bottom intermediate roll than otherwise possible with linear contact of the intermediate top and bottom rolls without aprons.
Drafting arrangements of this type are associated with the disadvantage that the contact zone covered by the arc length of the top apron at the bottom intermediate roll is limited due to the roll arrangement of the drafting arrangement and upstream and downstream of the nip of the pair of intermediate rolls only a limited arc can be utilized for guiding the roving.
On the other hand, a large wrapping angle at the intermediate roll would be disadvantageous, since then the roving would be sharply deflected while entering and leaving the zone between the apron and the intermediate roll instead of meeting the roll tangentially.
Widespread applications have been found for apron drafting arrangements of the type in which the aprons are deflected downstream by a deflecting rail, the second deflecting being effected by the intermediate rolls themselves. In order to obtain a long guiding zone with this arrangement the distance between the deflecting element and the intermediate roll is also chosen to be correspondingly large.
Such apron drafting arrangements exhibit considerable disadvantages since in the zone between the nip of the intermediate rolls and the deflecting elements the aprons are "pushed" and thus the danger of "wave formation" is exceptionally pronounced in this zone and the drafting zone of the roving can be disturbed. Additional tensioning springs provided for the aprons can counteract the "wave formation" to some extent, but with such measures the friction at the aprons is increased such that, on the one hand, the energy consumption of the apron drive increases and, on the other hand, the life of the aprons is unpermissibly shortened.